The present invention is related to a method to increase the oil production from an oil reservoir.
Recovery of oil from oil reservoirs under electrical stimulation has been described for instance in NO 161.697 and U.S. Pat. No. 4,884,594 as well as U.S. Pat. No. 5,282,508 corresponding to NO. appl. 922581.
The above patents is related to an enhanced oil recovery method currently known as the Eureka Enhanced Oil Recovery (EEOR) principle which is an enhanced oil recovery method specially designed for land-based oil fields. The principle is based on electrical and sonic stimulation of the oil-bearing strata in such a manner that the oil flow is increased.
This is done by introducing special vibrations into the strata. These vibrations will be as identical to the natural frequency of the rock matrix and/or the fluids as possible.
The vibrations give rise to several effects in the fluids and remaining gases in the strata. They decrease the cohesive and adhesive bonding, as well as a substantial part of the capillary forces, thereby allowing the hydrocarbons to flow more easily in the formation.
The vibrations that propagate into the reservoir as elastic waves will change the contact angle between the rock formation and the fluids, thereby reducing the hydraulic coefficient of friction. This allows a freer flow towards the wells where the velocity increases and creates a greater pressure drop around the well. The elastic waves give rise to an oscillating force in the strata, which results in different accelerations because of the different densities in the fluids. The fluids will xe2x80x9crubxe2x80x9d against each other because of the different accelerations to create frictional heat, which in turn reduces the surface tension on the fluids.
The vibrations also release trapped gas that contributes to a substantial gas lift of the oil. Furthermore, the oscillating force creates an oscillating sound pressure that contributes to the oil flow.
Heat is supplied to the reservoir to maintain and, at the same time, increase the pressure in the oil field when its natural pressure has been reduced. The heat is supplied both as frictional heat, from the vibrations, and also as alternating current into the wells. The electrical transmission capabilities always present in an oil field allow the alternating current to flow between wells to make the reservoir function in a manner similar to an electrode furnace because of resistance heating.
The heating causes a partial evaporation of the water and the lightest fractions of the hydrocarbons and remaining gases in the oil. Furthermore, the alternating current causes the ions in the fluids to oscillate and thereby creates capillary waves on the fluid interfaces and thus reduces the surface tensions, a phenomenon we have named xe2x80x9cThe in situ Electrified Surfactant Effect (IESE).
The heat created from the electrical stimulation and from the vibrations reduces the viscosity of the fluids.
The oil flow acts as a cooling medium that allows a greater energy density from the vibrator and the electricity supplied to the oil-producing wells.
A number of possibilities exist for the use of electricity to heat oil-bearing formations. These methods can be classified according to the dominant mechanism of thermal dissipation in the process. The line frequency plays a decisive role in how the electrical (and electromagnetic) energy is converted to heat. Dielectric heating prevails in the high-frequency range from radio frequencies to microwave frequencies. The dipoles formed by the molecules tend to align themselves with the electrical field. The alternation of this field induces a rotation movement of the dipoles with a velocity proportional to the alternation frequency. The molecular movement can be intense enough to produce considerable heat. A popular application of this process is in microwave ovens. Another possibility is inducing heating where the alternating electric current flows through a set of conductors, inducing a magnetic field in the medium. The variations of the magnetic fields, in turn, induce a secondary current whose circulation in the medium creates heat. This work is confined to the resistive heating process, which is the major mechanism when DC or low-frequency (up to 300 Hz) alternating current is used.
The electrical heating of a reservoir formation was used to enhance oil production as early as 1969, when an experiment in Little Tom, Tex., was successful. The production of four wells had increased from 1 bbl/d (0.16 m3/d) to an impressive average of 20 bbl/d (3.18 m3/d) for the experiment, which included wellbore fracturing. The method subsequently attracted the attention of an increasing number of investigators and engineers, and their field tests were reported within a few years. The first academic work on resistive heating was by El-Feky in 1977. He reported on the development and testing of a numerical model that was based on implicit-pressure, explicit-saturation formulation over a two-dimensional rectangular grid. Experimental data came from a laboratory model consisting of a five-spot water flood. The electrical concept was later coupled to water-injection processes to derive the so-called reservoir-selective-heating method.
Until 1986, the few existing reservoir simulators for the electrical enhanced process relied on explicit treatments to determine saturation, voltage, temperature, and pressure. Killough and Gonzales presented a fully explicit three-dimensional multicomponent model in 1986 that was capable of handling water vaporization. The authors focused on the idea of flood patterns for the heating water. In 1988, Watttenbarger and McDougal used a two-dimensional simulator to investigate the major parameters affecting the production response to electrical heating. They considered the steady-state regime to obtain a simple method for estimating the production rate.
Thomas Gordon Bell describes electroosmosis by electrolinking two or more oil wells In U.S. Pat. No. 2,799,641. William C. Pritchet describes a method and the apparatus for heating a subterranean formation by electrical conduction in U.S. Pat. No. 3,948,319. The method describes the use of alternating or direct current to preheat the formation.
Lloyd R. Kern describes the use of electricity to xe2x80x9cmeltxe2x80x9d hydrates (a typical methane hydrate have the chemical formulation CH4H2O) formed in typical arctic shallow formations.
E. R. Abernathy discusses the use of electromagnetic heating of the area near an oil well. [REF Journal of Canadian Petroleum Technology, July-September 1976, Montreal]
A. Herbert Harvey, M.D. Arnold and Samy A. El-Feky report a study of the usability of an electric current in the selective heating of a portion of an oil reservoir that is normally bypassed by injected fluid. [REF Journal of Canadian Petroleum Technology, July-September 1979, Montreal]
A. Herbert Harvey and M.D. Arnold describe a radial model for estimating heat distribution in selective electric reservoir heating. [REF Journal of Canadian Petroleum Technology, October-December, 1980, Montreal]
Erich Sarapuu describes a method in underground electrolinking by an impulse voltage to make cracks in the formation in U.S. Pat. No. 3,169,577.
The contribution of the different liquids to the pressure buildup depends on the original pressure, temperature and liquid/gas relationship in the reservoir. In a reservoir with low gas content, pressure and temperature, the main contribution to the increased pressure comes from evaporation of water and lighter crude fractions, and from thermal expansion of the gas.
The temperature and pressure increase occur not only in the vicinity of the well, but also between the wells, depending on the paths of the electrical potential between the well.
The energy input for each well depends on the oil flow and the set temperature in the bottom zone. This means that for a particular electrode (casing) temperature, which depends on the equipment, the power input depends on the cooling effect of the oil produced. The greater the oil production, the greater the energy input possible because the increased heat at the well area is drained away by the oil produced. If no oil is produced, the heat flow into the formation from the well would take place by heat conduction only.
The invention is drawn to a method for increasing the oil production from an oil reservoir. A magnetic or magnetostrictive material is injected into the end oil reservoir and then the material is vibrated with the aid of an alternative electric field. Oil is then drawn from the same oil reservoir from the same well in which the magnetic or magnetostrictive material was injected. The vibrations created in the injected material can be changed by changing the frequency of the applied electric current passed into the reservoir.